1. Field of the Invention
The present invention relates generally to an optical disk recording apparatus, and more particularly, to an improved optical disk recording apparatus for recording information on a write-once optical disk or an erasable optical disk.
2. Description of the Related Art
Conventionally, recordable optical disks break down into two general types: write-once and erasable/rewritable (hereinafter referred to as erasable). Further, there are two methods for recording information onto a write-once optical disk: using Te and Bi as the material for the signal recording surface and projecting a laser beam onto the surface of the disk to melt the surface to form pits thereon, and using Sb2, Se3 TeOx and a thin film of organic dye for the material for the signal recording surface, projecting a laser beam onto the surface of the disk and altering the reflection factor.
CD-R disks, which are write-once disks, are provided with guides called pregrooves. The pregroove wobbles slightly in a radial direction of the disk around a central frequency of 22.05 kHz, with recording time address information called ATIP (Absolute Time In Pregroove) recorded with FSK modulation at a maximum deviation of xc2x11 kHz.
With such CD-R disks, a recording power calibration process known as Optimum Power Control (OPC) is carried out in order to set the laser beam at an optimum recording power.
In order to facilitate an understanding of the present invention, a description will first be given of the OPC process in a conventional write-once optical disk recording apparatus.
FIG. 1 is a diagram illustrating an optical disk warp. As shown in FIG. 1, the recording surface of the optical disk includes a data area for recording a variety of data and a Power Calibration Area (indicated in the drawing as PCA) for test recordings in order to set the laser beam to optimum recording power.
The PCA is provided at the innermost track of the disk, and is in turn composed of a test area and a count area. The test area in turn is composed of 100 partitions, with each partition composed of 15 frames. In a single OPC operation a single partition is used, with test signals at 15 different levels of laser power being recorded, one signal (that is, one level) in each of the 15 frames. Thereafter peak (P) and bottom (B) values of an RF (high frequency) signal envelope generated from the test area are detected. Finally, that recording power level at which it is determined that a value beta (where beta=(P+B)/(Pxe2x88x92B)) exceeds some predetermined value (for example 0.04) is set as the optimum recording power.
The above-described setting of the optimum recording power at time of recording requires that the optimum recording power be set for each disk, because disk recording characteristics differ from one manufacturer to the next. It naturally follows that an inability to obtain the optimum recording power for each disk can lead to a sharp increase in post-recording error rate and jitter.
Furthermore, optical disk specification sheets observe that running OPC is conducted during information recording. Running OPC is a process in which the recording power is continuously monitored and adjusted as necessary, by comparing the intensity of the light reflected back from the pits in the surface of the optical disk when the optimum recording power was set during the OPC process with the intensity of the light reflected from the pits during information recording and correcting the recording power as appropriate based on the results of the comparison.
It should be noted that a pit having a time width of 11 T is used as the pit for obtaining the intensity of the reflected light (reference time width T is a standard speed, that is, at a speed of 1 X, approximately 230 nsec for one cycle at a frequency of 4.32 MHz), with the intensity of the light reflected from the rear edge of the pit being used for calibration.
As a result, the running OPC process can continuously adjust the laser recording power even as information is recorded on the disk moving radially from the inner periphery toward the outer periphery of the disk and as the optimum recording power varies from the optimum recording power set during the OPC process due to warpage of the optical disk and unevenness in sensitivity within the surface of the disk.
However, despite the use of running OPC to correct for variations in optimum recording power, the conventional art as described above has the following disadvantage.
Namely, most of the optical disks in question are recorded on one side only, so a certain amount of warpage is inevitable. Even so, the market is flooded with relatively heavily warped disks that have been perhaps poorly manufactured in a misguided effort to cut costs. With such disks the angle at which the recording laser light strikes the PCA located nearer the inner periphery of the optical disk 10 shown in FIG. 1 differs substantially from the angle at which the recording laser light strikes the data area that is located nearer the outer periphery of the optical disk 10, such that the laser light that is actually effective for recording differs from the laser light actually emitted from the object lens of the laser unit, and hence differs sharply from the optimum recording power.
The above-described problem is not of great concern when information is record on the optical disk continuously, that is, without interruption, from inner periphery to outer periphery during a so-called disk-at-once recording operation, because in that case the running OPC process described above works to ensure that the recording power is continuously corrected as necessary. However, in a case of so-called multi-session recording, in which information is not recorded continuously, a problem arises when recording of information commences again at an outer periphery of an area of the disk that has been recorded previously, because it typically requires a number of blocks before the running OPC function recommences operation, during which interval recording is conducted without benefit of correction of the laser power to optimum recording power, with a consequent failure to obtain optimum recording and a sharp increase in error rate and jitter.
Accordingly, it is an object of the present invention to provide an improved and useful optical disk recording apparatus and method, in which the above-described drawbacks and disadvantages are eliminated.
Another, further and more specific object of the present invention is to provide an improved and useful optical disk recording apparatus and method that can reduce degradation in recording conditions arising from variations in disk intrasurface sensitivity including disk warpage when adding information to an optical disk during multi-session recording of information
The above-described object of the present invention is achieved by an optical disk recording apparatus for recording information onto a write-once or erasable optical disk, the apparatus having a memory component, a correction component and a recording component. The memory component includes a table of prerecorded correction curves consisting of recording power correction values corresponding to radial positions for each type of a variety of different optical disks. The correction component continuously correcting as necessary the recording power using the appropriate correction value, in a process known as running OPC. The recording component records information onto the optical disk using the corrected recording power.
According to this aspect of the invention, degradation in recording conditions arising from variations in disk intrasurface sensitivity including disk warpage can be reduced and sharp deterioration in error rate and jitter can be eliminated so as to corrects the recording power obtained during OPC.